A capacitive pressure sensor used in, for example, measuring the pressure of a gas in a semiconductor manufacturing process or other processes includes a diaphragm joined to one end of a cylindrical body and an electrode member whose signal extraction side is fixed to the other end of the body with an insulator and having an electrode face opposed to the diaphragm with a gap between the diaphragm and the electrode face.
Such a capacitive pressure sensor has the following problem: the position of the electrode face in the body changes with a change in the position at which the signal extraction side of the electrode member is fixed, due to some reasons. Thus, the gap significantly deviates from a designed value, decreasing the measurement accuracy of pressure.
Moreover, Patent Literature 1 and FIG. 7 illustrate an example of a capacitive pressure sensor. More specifically, a capacitive pressure sensor 100A illustrated in FIG. 7 includes a body 1A, a diaphragm 2A, an electrode member 3AA, and an insulating positioning member 4A. The body 1A is substantially cylindrical, and is made of a metal such as stainless steel. The diaphragm 2A is joined to and blocks one end of the body 1A. The electrode member 3AA has an electrode face 3SA opposed to and a predetermined gap apart from the diaphragm 2A. The insulating positioning member 4A made of a glass, ceramic, or other materials is supported by the body 1A, and positions the electrode member 3AA in the body 1A.
The electrode member 3AA includes the electrode face 3SA, a signal extraction electrode 32A, and a spring 33A. The electrode face 3SA is a metal film evaporated onto the end face of the insulating positioning member 4A. The signal extraction electrode 32A is fixed with an insulating seal 6A that is a glass sealing the other end of the body 1A, and extracts a signal to the outside of the body 1A. The spring 33A electrically connects the electrode face 3SA and the signal extraction electrode 32A, and has one end fixed to the signal extraction electrode 32A. Such a structure is intended to inhibit a change in the gap between the diaphragm 2A and the electrode face 3SA due to the thermal deformation of the body 1.
However, in the structure in which the spring 33A connects the electrode face 3SA and the signal extraction electrode 32A as FIG. 7 illustrates, the spring 33A is exposed to the air. Thus, the spring 33A picks up electromagnetic noise, thereby deteriorating the signal-to-noise ratio of a signal obtained from the electrode face 3SA. This decreases the measurement accuracy of pressure.